With high integration of a semiconductor integrated circuit, a trend for patterns for LSI (Large Scale Integration) has recently become finer and more complex. The wavelength of deep ultraviolet light used in pattern's transfer is 193 nm whereas the size of a pattern to be transferred is shorter than the wavelength. With a demand for such miniaturization, a lithography technology has also become more advanced and complicated. To produce LSI in large quantity, the degree of freedom needed to design changes of mask patterns different for each product is also necessary for a lithography technology capable of transferring each pattern written on a mask which is an original picture onto a wafer. An electron beam lithography technology has therefore been used in pattern writing to the mask.
The electron beam lithography technology has an excellent resolution because an electron beam to be used is a charged particle beam. The electron beam lithography technology also has the advantage that it can suppress size fluctuations because the focal depth can be adjusted accurately. Therefore, the electron beam lithography technology has been in widespread use even in manufacturing of a mask or a reticle used when transferring an LSI pattern to a wafer. Further, an electron beam writing apparatus which directly writes patterns on a wafer using the electron beam lithography technology has been applied to the development of leading-edge devices, one typical example being a DRAM, another example, being used in part of the production of an ASIC.
The electron beam writing apparatus for realizing such an electron beam lithography technology is normally provided with a writing chamber which includes a stage for placing thereon a substrate (mask or wafer) target for writing, and an electronic lens barrel which applies an electron beam from an electron gun to the substrate placed on the stage.
Since the range in which the electron beam can be deflected and controlled is limited in the electron beam writing apparatus, each pattern is formed on the entire substrate by writing done while the substrate placed on the stage is being moved.
When writing is performed on the mask, a conductive material formed on the mask, e.g., a resist formed on a light shielding layer using chromium (Cr) becomes charged. If the writing continues in this state, then the trajectory of the electron beam is deflected due to an electric field created by the charged mask, thus resulting in an inability to perform writing to a desired position. It is therefore practice to ground a charged layer.
A substrate cover has been described in Japanese Patent Laid-open No. 2008-058809, which includes a frame which is formed larger in outer dimension than the outer peripheral end of a substrate in which a pattern will be written using an electron beam and formed with an opening at its central part in a size smaller than the outer peripheral end thereof, and earth pins which are provided on the lower side of the frame and make connections to the substrate. A configuration in which the substrate cover is disposed on its corresponding substrate to be subjected to writing has been described in Japanese Patent Laid-open No. 2008-058809. The substrate cover is formed entirely of a conductive metal material. Alternatively, one in which the surface of an insulating material such as a ceramic material or the like is coated with a conductive material is preferred as the substrate cover. Thus, according to the above configuration, the peripheral edge portion of the substrate is prevented from becoming charged, because electrons scattered in the neighborhood of the peripheral edge portion of the substrate are captured by the substrate cover.
The placement of such a substrate cover on the substrate such as the mask or the like is enabled by placing the substrate cover on the substrate outside the writing chamber before the substrate is carried in the writing chamber in which writing is done. In this case, it is preferable that a storage chamber for accommodating the substrate cover therein is provided outside the writing chamber, and the substrate cover can be attached onto the substrate in the storage chamber or detached therefrom. Incidentally, it is also possible to fix the substrate cover onto its corresponding stage in the writing chamber and place the substrate cover on the substrate in the writing chamber after the substrate has been carried in the writing chamber.
Thus, electron beam writing is performed on the substrate with the substrate cover placed thereon, on the stage in the writing chamber. In this case, in order to apply an electron beam to the substrate in the writing chamber and thereby perform writing with desired accuracy, the substrate is preferably positioned in the storage chamber. It is further necessary to position the substrate target for writing in the writing chamber before the irradiation of the electron beam.
FIG. 11 is a schematic diagram showing a configuration of a position detecting device applicable to a conventional electron beam writing apparatus.
In the conventional electron beam writing apparatus, such a position detecting device 210 having the configuration as shown in FIG. 11 can be used for positioning a substrate such as an object for writing. The position detecting device 210 includes an illumination device 211, a camera 213, an illumination controller 215, a camera controller 216, and a control device 220.
The position detecting device 210 is disposed in a writing chamber, detects a position of the substrate, and then locates the substrate. However, a method for positioning a substrate 200 with no above substrate cover placed thereon will be explained.
The illumination device 211 is disposed above or below the substrate 200 target for positioning and is capable of applying light in the direction perpendicular to the surface (upper surface) or back surface (lower surface) of the substrate 200. Then, the substrate 200 is disposed between the illumination device 211 and camera 213 of the position detecting device 210. Next, illumination light is applied to edge portion of the surface of the substrate 200 from above the substrate 200. Specifically, the illumination controller 215 is given a lighting instruction from the control device 220 which illuminates device 211.
The camera 213 takes an image near the edge portion of the substrate 200 in a state in which the illumination light has been applied from the illumination device 211. Specifically, the camera controller 216 given an imaging instruction from the control device 220 performs imaging through the camera 213. Then, the edge position of the substrate 200 is detected to locate the substrate.
Although the configuration of the position detecting device 210 applicable to the conventional electron beam writing apparatus, and the method for the positioning the substrate 200 using the same are as described above, a problem arises where an attempt is made to apply this to the substrate on which the substrate cover is placed.
Namely, when the substrate cover (not shown) is placed on the substrate 200 target for writing, this becomes a light shielding canopy, thereby interfering with the application of the illumination light from the illumination device 211 to the edge portion of the substrate 200 located below the substrate cover.
As a result, the camera 213 opposite to the illumination device 211 with the substrate 200 interposed in between is not capable of imaging the edge portion of the substrate 200, thus making it unable to position the substrate edge and, as a result, the substrate 200.
A position detecting device has been described in Japanese Patent Laid-open No. 2008-210951 which includes another illumination device for irradiating a substrate with light in a direction parallel to the front and back surfaces of the substrate as viewed from a lateral direction in addition to an illumination device lying above the substrate. The position detecting device enables the detection of a substrate's edge position.
In the position detecting device described in Japanese Patent Laid-open No. 2008-210951, even if the substrate cover described above is placed on the substrate, the application of light to the substrate's edge portion is enabled by the irradiation of the illumination light from the lateral direction, so that the positioning of the substrate is made possible.
When, however, an attempt is made to apply the illumination light to the substrate only by the irradiation of the illumination light from the lateral direction, an image to be taken by a camera may be affected by the shape of the side portion of the substrate and the degree of chamfering of the substrate. Namely, when a film such as a resist formed on the substrate is rounded on the side face of the substrate, light dependent on the shape of a film portion at the side portion thereof and reflected by that portion may enter the camera located below the substrate, so that this may affect the imaging of the substrate edge.
According to the degree of chamfering at the side surface of the substrate, light reflected thereby may enter the camera lying below the substrate, so that this may affect the imaging of the substrate edge. In such a case, it is not possible to perform the accurate imaging of the edge portion, by extension, the accurate positioning of the substrate as compared with the case in which the illumination light is applied from above.
When an attempt is made to apply such a position detecting device described in Japanese Patent Laid-open No. 2008-210951 to the storage chamber of the substrate described above, it is necessary to position the substrate before and after the placement of the substrate cover onto the substrate. However, the substrate edge is imaged by illumination from above the substrate before the placement of the substrate cover thereon, whereas after the placement of the substrate cover thereon, the substrate edge is imaged by illumination from the direction of the side surface of the substrate. It is thus not possible to perform, within the storage chamber, the positioning of the substrate by the same method before and after the placement of the substrate cover. In such a case, the operation of positioning the substrate becomes complicated, and there is a need to detect the substrate edge by properly using two methods different in accuracy, thus resulting in an inability to perform the accurate positioning of the substrate.
Likewise, it is not possible to accurately determine the positioning between the substrate cover and the substrate on which the substrate cover is placed. Namely, even if the substrate cover is shifted while being placed on the substrate, it is not possible to accurately detect its shift.
When the position of the placement of the substrate cover is displaced, the position of the substrate cover on the substrate changes from a predetermined position, and thereby the position of writing on the substrate may be degraded. In order to prevent degradation of such a writing position, there is a need to control the position between the substrate and the substrate cover in the order of about a few μm to about a few tens of μm, for example.
When the position of the placement of the substrate cover with respect to the substrate is displaced from a predetermined position, there is a case in which the potential of the surface of the substrate at the time of electron beam writing changes and the influence on the accuracy of writing to the substrate cannot be ignored.
The accuracy of writing to the substrate needs an nm order. It is necessary to reduce a relative position displacement between the substrate and the substrate cover, corresponding to one factor that causes an error, and control the positioning between the substrate and the substrate cover.
Incidentally, when an attempt is made to place the substrate cover on the substrate within the writing chamber as described above, it is not possible to perform the positioning of the substrate with desired accuracy and control the positioning between the substrate and the substrate cover with desired accuracy.
Accordingly, there has been a demand for the development of a substrate cover, particularly a substrate cover disposed on a substrate in its use, wherein the substrate will be subjected to pattern writing later using an electron beam such as a charged particle beam, the substrate cover enabling more accurate positioning of the substrate and thereby enabling the positioning of the substrate by irradiation of light from above the substrate.
The present invention has been made in view of such problems. Namely, an object of the present invention is to provide a substrate cover which enables the application of light to the edge portion of a substrate by light irradiation means provided above the substrate and consequently enables the detection of a position of the edge portion of the substrate by a light detecting device provided below the substrate. The object of the present invention is to provide a charged particle beam writing method which enables the positioning of a substrate target for writing with desired accuracy using this novel substrate cover, enables the control of the positioning between the substrate and the substrate cover with desired accuracy, and enables the realization of a desired pattern size and pattern accuracy. Other advantages and challenges of the present invention are apparent from the following description.